A Port Macquarie swim coach has outlined the task ahead for a devastated James Magnussen as he tries to shrug off a disappointing relay swim and prepare for the 100 metres freestyle.

Magnussen swam 48.03 in the lead swim for the fourth placed Aussies.

Michael Mullins is the manager at Port Macquarie pool and coached Magnussen as a junior.

He says "the Missile" now faces an uncomfortable two days before the 100 metre heats and it won't be easy for the young man to lift himself mentally for the next challenge.

"It's going to be hard.

"Obviously he needs to sit back and re-evaluate and maybe try and find out what went wrong," he said.

"In two days, a lot of things change.

"He's just got to sort of get back and re-evaluate where he went wrong and try and lift again you know," he said.

"You've got a bloke like Laurie Lawrence over there, one of the greatest motivators in the world, maybe he needs to get in James' ear and say listen here big fella you know and try to lift him out of that lull.

Mr Mullins says the young swim star has some big hurdles to overcome in the coming days.

Magnussen's swim in the 4 x 100 metre relay was a full second slower than his best, shocking the nation, his coach and himself.

Mr Mullins says he's at a loss to understand what went wrong.

He says preparing mentally for the 100 metres freestyle over the next few days will be a challenge for Magnussen.

"His coach would be absolutely lost as well, he would be trying to find words to say.

"You know I just think he's got to do it himself," he said.

"No-one's going to do it for him, so he's just got to lift.

"We know he's capable of doing it, but whether he can put it back together again?

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